A thyristor is a semiconductor device used as a switch in power control applications. Typically, thyristors are comprised of multiple layers of P-type semiconductor material and N-type semiconductor material. Various types of thyristors include, among others, silicon controlled rectifiers (SCRs), triacs, sidacs, diacs, and transient surge protection devices. These devices differ from each other in the number of layers of P-type and N-type semiconductor material and in the number of terminals each has. For example, a silicon controlled rectifier (SCR) is a four layer semiconductor device that has three terminals, a triac is a five layer semiconductor device that has three terminals, a sidac is a five layer semiconductor device that has two terminals, and a diac is a three layer semiconductor device that has two terminals. As a further example, FIG. 1 is a cross-sectional view of a prior art SCR 10 that has a base region 12 of N-type conductivity sandwiched between gate and anode regions 14 and 16, respectively, of P-type conductivity. Gate region 14 is formed within a mesa structure 17 and anode region 16 is formed within a mesa structure 19. A cathode region 18 of N-type conductivity is formed within gate region 14. SCR 10 is configured such that an NPN transistor is formed from base region 12, gate region 14, and cathode region 18 and a PNP transistor is formed from anode region 16, base region 12, and gate region 14.
SCR 10 can be biased to operate in a forward operating mode or a reverse operating mode. In the forward operating mode, a positive voltage is applied to anode region 16 and a negative voltage is applied to cathode region 18. When a positive voltage is applied to gate region 14, the NPN transistor formed from base region 12, gate region 14, and cathode region 18 turns on which then turns on the PNP transistor formed from gate region 14, base region 12, and anode region 16.
In the absence of a bias voltage at gate region 14, the P-N junction between base region 12 and gate region 14 is reverse biased and a leakage current flows across the junction formed by gate region 14 and base region 12. The leakage current lowers the breakdown voltage of SCR 10, which decreases its reliability. In addition, the leakage current decreases the yield which increases the cost of manufacturing a thyristor such as, for example, SCR 10.
Hence, a need exists for a thyristor having a decreased reverse leakage current and improved reliability and a method of manufacturing the thyristor. Further, it would be advantageous for the thyristor to be cost efficient to manufacture.